In many systems composed of two or more metallic elements there may appear, under some conditions of composition and temperature, phases other than the primary solid solutions which are commonly known as intermediate phases. Many intermediate phases are referred to by means of a Greek symbol or formula, e.g., Cu.sub.3 Al, CuZn and Mg.sub.2 Pb, or both, although it is generally observed that many such so-called stoichiometric intermediate phases exist over a range of temperatures and compositions. Occasionally, as in the case of Mg.sub.2 Pb found in the Mg-Pb system, a true practically completely ordered stoichiometric compound is formed which is properly called an intermediate compound. If, in addition, the elements of the compound are regarded as metallic, the intermediate compound is commonly called an intermetallic compound.
Intermediate phases often exhibit properties entirely different from those of the component metals comprising the system and frequently have complex crystallographic structures. The lower order of crystal symmetry and fewer planes of dense atomic population of those complex crystallographic structures may be associated with the differences in properties, e.g., greater hardness, lower ductility, and lower electrical conductivity of the intermediate phases compared to the properties of the primary (terminal) solid solutions.
Although several intermetallic compounds with otherwise desirable properties, e.g., hardness, strength, stability, and resistance to oxidation and corrosion at elevated temperatures, have been identified, their characteristic lack of ductility has posed formidable barriers to their use as structural materials.
Recently, as described by Aoki and Izumi in the Journal of the Japan Institute of Metals (vol. 43, p. 358, 1979), microalloying of the intermetallic phase Ni.sub.3 Al with trace amounts of boron (0.05 and 0.1 wt. %) proved successful in increasing the ductility of that otherwise brittle and non-ductile intermetallic. Although the room temperature tensile strain at fracture of the Ni.sub.3 Al with boron was improved to about 35%, compared to about 3% for Ni.sub.3 Al without boron, the room temperature yield strength remained at about 30 ksi.
It would be highly desirable if there were available a simple, direct method by which both the strength and the ductility of intermetallic phases could be increased while maintaining or improving upon the desirable attributes of the intermetallic phases such as stability and resistance to oxidation and corrosion at elevated temperatures.